Regenerate it
Kuzan (Aokiji) is close behind, and by some trackers has actually matched or edged past Sakazuki, landing in roughly the same $1,150-1,600 band
new cards allow the game to add new ideas, increase the card pool for a multitude of strategies as well as create never-before-seen strategies, and give us more examples of vanilla creatures used to teach people how to draft
Five mana is a bit steep but in the late game it matters a lot less about the cost and a lot more about the immediate impact, this flexibility makes the card much stronger rather like Mull Drifter which is somewhat of a back up plan in one of its curve slots
Like most Pokmon cards, the value of Mudkip depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Emerald)